Correction magnets for cathode-ray tubes and methods for magnetizing same



Sept. 7, 1965 E. A. STEINGRQEVER CORRECTION MAGNETS FOR GATHODE-RAYTUBES AND METHODS FOR MAGNETIZING SAME Filed July 5, 1961 aqfi/apfFmiz'iaf 129250270 3x175 CZ/e/ur/m/v ran gas United States Patent3,205,414 CORRECTION MAGNETS FOR CATHODE RAY gUBES AND METHODS FORMAGNETIZING Erich A. Steingroever, Bonn (Rhine), Germany, assignor toMagnetfabrik Bonn Gewerkschaft Windhorst, Bonn, Germany Filed July 3,1961, Ser. No. 121,444 Claims priority, application Germany, July 6,1960, M 45,842 8 Claims. (Cl. 317-200) The invention relates to amagnetic focussing device for the electron beam of a cathode ray tubeand is particularly suitable for such tubes in television receivers.

It is known to use permanent ring magnets which are positioned aroundthe cathode ray tube neck and produce a magnetic field of severaloersted transversely of the direction of the electron beam. By turningsuch socalled correctionrings, the influence of external fields and ofthe magnetic earth field on the position of the image can be corrected.For manipulation, the rings are provided with handles projecting intothe plane of the structure.

The known correction rings may consist of a plastic base in which anannular wire of permanent magnetic material is embedded.

Heretofore, it has not been possible to produce such correction rings ina simple procedure only from a magnetic powder and binder as integralstructures where also the handles consist of magnetic material. Thereason was that, on magnetizing, also said handles became magnetic andproduced a distortion of the magnetic field in the center of the ring.

The invention eliminates said drawback and makes it possible tomanufacture correction rings of the type described by an injection orcompression molding process as single integral units. In accordance withthe invention, only the annular part of the correction rings ismagnetized while the manipulating handles are not magnetized or only solittle as not to interfere with the correcting field.

In a preferred embodiment of the invention, the operating handles arearranged in the neutralzone of the correction rings. Such arrangementmakes the magnetic stray field, with respect to the center of the ring,very small; in addition, it may eliminate the need of a specific shieldduring magnetization, or a demagnetization of the handles.

The invention will be described with reference to the accompanyingdrawings, in which FIG. 1 shows, diagrammatically, an axial sectionalview of magnetic correction rings around the neck of a cathode ray tube;

FIG. 2 shows a view of a magnetic correction ring according to theinvention;

FIG. 3 shows the arrangement for magnetizing the rings, and

FIG. 4 is a view of a modification of the ring shown in FIG. 2. a

As it will be seen from FIG. 1 preferably two coaxial spaced correctionrings are used which can be rotatably displaced with respect to eachother to adjust the strength and direction of the correction field.

Each correction ring 1 is prepared from a mixture of a magnetic powderand a thermoplastic binder, for instance in a die casting procedure. Thering is magnetized by means of a magnetizing coil 2 from the inside soas to form a magnetic field in direction of the arrow N-S, which fieldruns in the ring approximately along the broken lines. Duringmagnetization, the two manipulating handles 3 and 4 are surrounded bythe sheet iron sleeves 5 and 6, so that they remain substantially un-3,205,414 Patented Sept. 7, 1965 Said sleeves are removed aftermagnetization.

Instead of using sheet iron sleeves 5 and 6, the manipulating handles orother projections extending beyond the circular periphery of the ringmay be protected, during magnetization, by means of sleeves made of agood electrically conducting material, for instance of copper oraluminum. It is also possible to prevent magnetizing of said projectionsduring the magnetizing operations by means of additional coils;preferably, such additional coils are arranged in series with the mainmagnetizing coil and compensate the magnetizing field at theprojections.

It is also possible to magnetize the correction rings without specialprecautions. In such a case, the interfering projections or manipulatinghandles may be subsequently demagnetized.

In another embodiment of the invention, interference of the manipulatinghandles with the correction field is minimized by arranging said handles(7, 8 in FIG. 4) in the neutral zone of the correction rings. In thisarrangement, the magnetic stray field of the projections with relationto the center of the ring becomes so weak that a special shieldingduring magnetizing, or demagnetization, can be omitted.

I prefer to make the manipulating handles of the two rings of differentsize ,or form to facilitate distinguishing the one ring from the other.

Any magnetic material may be employed for the correction rings. I preferto make the rings by injection molding of a permanent magnetic powder asdisclosed in my copending application Ser. No. 92,912, filed March 2,1961, for a Magnetic Composition. Said pennanent magnetic materials aremixtures of a non-magnetic thermoplastic binder with particles of thetype and alloys known under the names Alni and Alnico, which have thefollowing composition:

or PbO-6Fe O may be used.

As non-magnetic binders, any thermoplastic resin such as homopolymers.or copolymers of vinyl chloride, polyarnides, cellulose acetate, alsonatural or synthetic rubbers, may be used. I prefer to employ apolyalkylene like polyethylene.

Iclaim:

1. A permanent magnetic device for a cathode-ray tube neck comprising acorrection ring having a magnetized annular portion adapted to surroundsaid neck and a manipulating handle projecting from the outer peripheryof said annular portion, said annular portion and handle forming aunitary structure made of the same magnetic composition, saidmanipulating handle having a magnetic characteristic causingsubstantially no interference with the magnetic field of said annularportion.

2. A magnetic device as claimed in claim 1 wherein said handle isarranged in the magnetically neutral zone of the ring.

3. A magnetic device as claimed in claim 1 wherein said annular portionand handle consist essentially of a mixture of a non-magneticthermoplastic resin binder with a member of the group consisting ofnickel-aluminum-iron alloys and ferrites MO-6Fe O wherein M is a memberof the group consisting of Ba, Sr, and Pb.

4. A magnetic correction device for a cathode ray tube comprising a pairof coaXially spaced magnetized correction rings to surround the neck ofsaid tube and supported for rotatable displacement of one ring to theother, each of said rings having a manipulating handle projecting fromthe outer periphery thereof, the annular portions of said rings and saidhandles forming a unitary structure made of the same magneticcomposition, and said manipulating handles each having a magneticcharacteristic causing substantially no interference with the magneticfield ,of said annular portions.

5. A device as claimed in claim 4 wherein the handles of said rings havedilferent size.

6. A device as claimed in claim 4 wherein the handles of said rings havediiferent form.

7. The method of magnetizing magnetic correction rings for cathode raytubes, which rings are provided with'integral projecting handles of thesame material as said rings, comprising the steps of shielding saidhandles References Cited by the Examiner UNITED STATES PATENTS2,542,924: 2/51 Heppner 317200 2,817,034 12/57 Covill 317200 2,922,9081/ Heller 317-200 2,950,407 8/60 Barkow et al. 31384 FOREIGN PATENTS489,657 1/z53 Canada. 85 8,627 1/ 61 Great Britain.

LARAMIE E. ASKIN, Acting Primary Examiner.

SAMUEL BERNSTEIN, JOHN F. BURNS, Examiners.

1. A PERMANENT MAGNETIC DEVICE FOR A CATHODE-RAY TUBE NECK COMPRISING ACORRECTION RING HAVING A MAGNETIZED ANNULAR PORTION ADAPTED TO SURROUNDSAID NECK AND A MANIPULATING HANDLE PROJECTING FROM THE OUTER PERIPHERYOF SAID ANNULAR PORTION, SAID ANNULAR PORTION AND HANDLE FORMING AUNITARY STRUCTURE MADE OF THE SAME MAGNETIC COMPOSITION, SAIDMANIPULATING HANDLE HAVING A MAGNETIC CHARACTERISTIC CAUSINGSUBSTANTIALLY NO INTERFERENCE WITH THE MAGNETIC FIELD OF SAID ANNULARPORTION.
 7. THE METHOD OF MAGNETIZING MAGNETIC CORRECTION RINGS FORCATHODE RAY TUBES, WHICH RINGS ARE PROVIDED WITH INTEGRAL PROJECTINGHANDLES OF THE SAME MATERIAL AS SAID RINGS, COMPRISING THE STEPS OFSHIELDING SAID HANDLES FROM MAGNETIC EFFECTS AND MAGNETIZING THE ANNULARPORTION OF SAID RING WHILE SAID HANDLE IS SHIELDED.